Virilization of the urogenital sinus of the tammar wallaby is not unique to 5alpha-androstane-3alpha,17beta-diol

FOXA1 and SOX9 Expression in the Developing Urogenital Sinus of the Tammar Wallaby (Macropus eugenii)

The mammalian prostate is a compact structure in humans but multi-lobed in mice. In humans and mice, FOXA1 and SOX9 play pivotal roles in prostate morphogenesis, but few other species have been examined. We examined FOXA1 and SOX9 in the marsupial tammar wallaby, Macropus eugenii, which has a segmented prostate more similar to human than to mouse. In males, prostatic budding in the urogenital epithelium (UGE) was initiated by day 24 postpartum (pp), but in the female the UGE remained smooth and had begun forming the marsupial vaginal structures. FOXA1 was upregulated in the male urogenital sinus (UGS) by day 51 pp, whilst in the female UGS FOXA1 remained basal. FOXA1 was localised in the UGE in both sexes between day 20 and 80 pp. SOX9 was upregulated in the male UGS at day 21-30 pp and remained high until day 51-60 pp. SOX9 protein was localised in the distal tips of prostatic buds which were highly proliferative. The persistent upregulation of the transcription factors SOX9 and FOXA1 after the initial peak and fall of androgen levels suggest that in the tammar, as in other mammals, these factors are required to sustain prostate differentiation, development and proliferation as androgen levels return to basal levels.

Development of the penile urethra in the tammar wallaby

Hypospadias is increasingly common, and requires surgery to repair, but its aetiology is poorly understood. The marsupial tammar wallaby provides a unique opportunity to study hypospadias because penile differentiation occurs postnatally. Androgens are responsible for penile development in the tammar, but the majority of differentiation, in particular formation and closure of the urethral groove forming the penile urethra in males, occurs when there is no measurable sex difference in the concentrations of testosterone or dihydrotestosterone in either the gonads or the circulation [corrected]. Phalluses were examined morphologically from the sexually indifferent period (when androgens are high) to well after the time that the phallus becomes sexually dimorphic. We show that penile development and critical changes in the positioning of the urethra occur in the male phallus begin during an early window of time when androgens are high. Remodelling of the urethra in the male occurs between days 20-60. The critical period of time for the establishment urethral closure occurs during the earliest phases of penile development. This study suggests that there is an early window of time before day 60 when androgen imprinting must occur for normal penile development and closure of the urethral groove.

The critical role of androgens in prostate development

Androgens are involved in every aspect of prostate development, growth, and function from early in male embryogenesis to prostatic hyperplasia in aging men and dogs. Likewise, androgen deprivation at any phase of life causes a decrease in prostate cell number and DNA content. The process by which the circulating androgen testosterone is converted to dihydrotestosterone in the tissue and dihydrotestosterone in turn gains access to the nucleus where it regulates gene expression, largely via interaction with a receptor protein, is understood, but the downstream control mechanisms by which hormonal signals are translated into differentiation, growth, and function are being unraveled.

5alpha-androstane-3alpha,17beta-diol supports human prostate cancer cell survival and proliferation through androgen receptor-independent signaling pathways: implication of androgen-independent prostate cancer progression

Androgen and androgen receptor (AR) are involved in growth of normal prostate and development of prostatic diseases including prostate cancer. Androgen deprivation therapy is used for treating advanced prostate cancer. This therapeutic approach focuses on suppressing the accumulation of potent androgens, testosterone and 5alpha-dihydrotestosterone (5alpha-DHT), or inactivating the AR. Unfortunately, the majority of patients with prostate cancer eventually advance to androgen-independent states and no longer respond to the therapy. In addition to the potent androgens, 5alpha-androstane-3alpha,17beta-diol (3alpha-diol), reduced from 5alpha-DHT through 3alpha-hydroxysteroid dehydrogenases (3alpha-HSDs), activated signaling may represent a novel pathway responsible for the progression to androgen-independent prostate cancer. Androgen sensitive human prostate cancer LNCaP cells were used to compare 5alpha-DHT and 3alpha-diol activated androgenic effects. In contrast to 5alpha-DHT, 3alpha-diol regulated unique patterns of beta-catenin and Akt expression as well as Akt phosphorylation in parental and in AR-silenced LNCaP cells. More significantly, 3alpha-diol, but not 5alpha-DHT, supported AR-silenced LNCaP cells and AR negative prostate cancer PC-3 cell proliferation. 3alpha-diol-activated androgenic effects in prostate cells cannot be attributed to the accumulation of 5alpha-DHT, since 5alpha-DHT formation was not detected following 3alpha-diol administration. Potential accumulation of 3alpha-diol, as a result of elevated 3alpha-HSD expression in cancerous prostate, may continue to support prostate cancer growth in the presence of androgen deprivation. Future therapeutic strategies for treating advanced prostate cancer might need to target reductive 3alpha-HSD to block intraprostatic 3alpha-diol accumulation.

Pre-receptor regulation of the androgen receptor

The human androgen receptor (AR) is a ligand-activated nuclear transcription factor and mediates the induction of genes involved in the development of the male phenotype and male secondary sex characteristics, as well as the normal and abnormal growth of the prostate. We have identified the pair of hydroxysteroid dehydrogenases (HSDs) that regulate ligand access to the AR in human prostate. We find that type 3 3alpha-HSD (aldo-keto reductase (AKR)1C2) catalyzes the NADPH dependent reduction of the potent androgen 5alpha-dihydrotestosterone (5alpha-DHT) to yield the inactive androgen 3alpha-androstanediol (3alpha-diol). We also find that RoDH like 3alpha-HSD (RL-HSD) catalyzes the NAD(+) dependent oxidation of 3alpha-diol to yield 5alpha-DHT. Together these enzymes are involved in the pre-receptor regulation of androgen action. Inhibition of AKR1C2 would be desirable in cases of androgen insufficiency and inhibition of RL-HSD might be desirable in benign prostatic hyperplasia.

The functional development of Leydig cells in a marsupial

Leydig cells are the major source of androgen in the male mammal. We describe here for the first time the development of the Leydig cell in a macropodid marsupial, the tammar wallaby, Macropus eugenii. Leydig cells are first recognized morphologically 2 days after birth with the appearance of lipid droplets in the cytoplasm of certain interstitial cells. Lipid content closely matches the steroid content of the developing testis and marks the maturation of the steroid synthesis pathway in the tammar testis. Morphologically mature Leydig cells, marked by distinct mitochondria with tubular cristae and an extensive anastomosing network of smooth endoplasmic reticulum, are developed by day 10 after birth - the time of peak testosterone content in perinatal tammar testes. The volume percentage of each cell type in the testis does not change over time so the growth of each cellular component keeps pace with growth of the whole testis. There was no morphological or quantitative evidence of a change from one population of Leydig cells to another in the tammar testis as has been reported in several other species including the rat, mouse and human. Maturation of the testis is also marked by the development of tight junctions between the cell membranes of adjacent Sertoli cells. These appear around day 30 after birth and coincide with the onset of mitotic arrest in male germ cells. Overall, the development of the Leydig cell in the tammar wallaby follows a similar pattern to that seen in other mammals, although the start of Leydig cell differentiation is, like many other organ systems in marsupials, post natal, not fetal and there appears to be only a single population of Leydig cells.

Androgen actions and the ovary

Although androgens and the androgen receptor (AR) have defining roles in male reproductive development and function, previously no role in female reproductive physiology beyond testosterone (T) as the precursor in estradiol (E(2)) biosynthesis was firmly established. Understanding the role and specific mechanisms of androgen action via the AR in the ovary has been limited by confusion on how to interpret results from pharmacological studies, because many androgens can be metabolized in vivo and in vitro to steroids that can also exert actions via the estrogen receptor (ESR). Recent genetic studies using mouse models with specific disruption of the Ar gene have highlighted the role that AR-mediated actions play in maintaining female fertility through key roles in the regulation of follicle health, development, and ovulation. Furthermore, these genetic studies have revealed that AR-mediated effects influence age-related female fertility, possibly via mechanisms acting predominantly at the hypothalamic-pituitary axis in a dose-dependent manner. This review focuses on combining the findings from pharmacological studies and novel genetic mouse models to unravel the roles of ovarian androgen actions in relation to female fertility and ovarian aging, as well as creating new insights into the role of androgens in androgen-associated reproductive disorders such as polycystic ovarian syndrome.

Society for Reproductive Biology Founders' Lecture 2006 - life in the pouch: womb with a view

Marsupials give birth to an undeveloped altricial young after a relatively short gestation period, but have a long and sophisticated lactation with the young usually developing in a pouch. Their viviparous mode of reproduction trades placentation for lactation, exchanging the umbilical cord for the teat. The special adaptations that marsupials have developed provide us with unique insights into the evolution of all mammalian reproduction. Marsupials hold many mammalian reproductive 'records', for example they have the shortest known gestation but the longest embryonic diapause, the smallest neonate but the longest sperm. They have contributed to our knowledge of many mammalian reproductive events including embryonic diapause and development, birth behaviour, sex determination, sexual differentiation, lactation and seasonal breeding. Because marsupials have been genetically isolated from eutherian mammals for over 125 million years, sequencing of the genome of two marsupial species has made comparative genomic biology an exciting and important new area of investigation. This review will show how the study of marsupials has widened our understanding of mammalian reproduction and development, highlighting some mechanisms that are so fundamental that they are shared by all today's marsupial and eutherian mammals.

Transcript profiling of the androgen signal in normal prostate, benign prostatic hyperplasia, and prostate cancer

Human prostate adenocarcinoma (CaP) and benign prostatic hyperplasia (BPH) have epithelial and stromal cell origins, respectively. To determine whether the androgen signal is processed differently in these cell types the expression of transcripts for enzymes that control ligand access to the androgen receptor (AR) were measured. Transcripts for type 2 5alpha-reductase, ketosteroid reductases [aldo-keto reductase (AKR)1C1-AKR1C4], the major oxidative 3alpha-hydroxysteroid dehydrogenase (HSD) retinol dehydrogenase (RODH)-like 3alpha-HSD (RL-HSD) and nuclear receptors [AR, estrogen receptor (ER)alpha, and ERbeta] were determined in whole human prostate and in cultures of primary epithelial cells (PEC) and primary stromal cells (PSC) from normal prostate, CaP and BPH by real-time RT-PCR. Normal PEC (n=14) had higher levels of AKR1C1 (10-fold, P<0.001), AKR1C2 (115-fold, P<0.001) and AKR1C3 (6-fold, P<0.001) than normal PSC (n=15), suggesting that reductive androgen metabolism occurs. By contrast, normal PSC had higher levels of AR (8-fold, P<0.001) and RL-HSD (21-fold, P<0.001) than normal PEC, suggesting that 3alpha-androstanediol is converted to 5alpha-dihydrotestosterone to activate AR. In CaP PEC (n=14), no significant changes in transcript levels vs. normal PEC were observed. In BPH PSC (n=21) transcripts for AR (2-fold, P<0.001), AKR1C1 (4-fold, P<0.001), AKR1C2 (10-fold P<0.001), AKR1C3 (4-fold, P<0.001) and RL-HSD (3-fold, P<0.003) were elevated to increase androgen response. Differences in the AR:ERbeta transcript ratios (eight in normal PEC vs. 280 in normal PSC) were maintained in PEC and PSC in diseased prostate. These data suggest that CaP may be more responsive to an ERbeta agonist and BPH may be more responsive to androgen ablation.

Differential expression of WNT4 in testicular and ovarian development in a marsupial

Background

WNT4 is a key regulator of gonadal differentiation in humans and mice, playing a pivotal role in early embryogenesis. Using a marsupial, the tammar wallaby, in which most gonadal differentiation occurs after birth whilst the young is in the pouch, we show by quantitative PCR during early testicular and ovarian development that WNT4 is differentially expressed ingonads.

Results

Before birth, WNT4 mRNA expression was similar in indifferent gonads of both sexes. After birth, in females WNT4 mRNA dramatically increased during ovarian differentiation, reaching a peak by day 9–13 post partum (pp) when the ovarian cortex and medulla are first distinguishable. WNT4 protein was localised in the ovarian cortex and at the medullary boundary. WNT4 mRNA then steadily decreased to day 49, by which time all the female germ cells have entered meiotic arrest. In males, WNT4 mRNA was down-regulated in testes immediately after birth, coincident with the time that seminiferous cords normally form, and rose gradually after day 8. By day 49, when testicular androgen production normally declines, WNT4 protein was restricted to the Leydig cells.

Conclusion

This is the first localisation of WNT4 protein in developing gonads and is consistent with a role for WNT4 in steroidogenesis. Our data provide strong support for the suggestion that WNT4 not only functions as an anti-testis gene during early development, but is also necessary for later ovarian and testicular function.

Ontogeny and pathway of formation of 5alpha-androstane-3alpha,17beta-diol in the testes of the immature brushtail possum Trichosurus vulpecula

The testicular androgen 5alpha;-androstane-3alpha,17beta-diol (androstanediol) mediates virilisation in pouch young of a marsupial, the tammar wallaby, and is the principal androgen formed in immature rodent testes. To chart the pattern of androstanediol formation in another marsupial species, the testes or fragments of testes from brushtail possums (Trichosurus vulpecula) that spanned the age range from early pouch young to mature adults were incubated with (3)H-progesterone and the products were identified by high-performance liquid chromatography. The only 19-carbon steroids identified in pouch young and adult testes were the Delta(4)-3-keto-steroids testosterone and androstenedione. However, androstanediol and another 5alpha-reduced androgen (androsterone) were synthesised by testes from Day 87-200 males and these appeared to be formed from the 5alpha-reduction and 3-keto reduction of testosterone and androstenedione. In the prostate and glans penis of the immature male, (3)H-androstanediol was converted to dihydrotestosterone. We conclude that the timing of androstanediol formation in the possum testis resembles the process in rodents rather than in the tammar wallaby and that any androstanediol in the circulation probably acts in target tissues via conversion to dihydrotestosterone.

Identification of the Major Oxidative 3α-Hydroxysteroid Dehydrogenase in Human Prostate That Converts 5α-Androstane-3α,17β-diol to 5α-Dihydrotestosterone: A Potential Therapeutic Target for Androgen-Dependent Disease

Androgen-dependent prostate diseases initially require 5α-dihydrotestosterone (DHT) for growth. The DHT product 5α-androstane-3α,17β-diol (3α-diol), is inactive at the androgen receptor (AR), but induces prostate growth, suggesting that an oxidative 3α-hydroxysteroid dehydrogenase (HSD) exists. Candidate enzymes that posses 3α-HSD activity are type 3 3α-HSD (AKR1C2), 11-cis retinol dehydrogenase (RODH 5), L-3-hydroxyacyl coenzyme A dehydrogenase , RODH like 3α-HSD (RL-HSD), novel type of human microsomal 3α-HSD, and retinol dehydrogenase 4 (RODH 4). In mammalian transfection studies all enzymes except AKR1C2 oxidized 3α-diol back to DHT where RODH 5, RODH 4, and RL-HSD were the most efficient. AKR1C2 catalyzed the reduction of DHT to 3α-diol, suggesting that its role is to eliminate DHT. Steady-state kinetic parameters indicated that RODH 4 and RL-HSD were high-affinity, low-capacity enzymes whereas RODH 5 was a low-affinity, high-capacity enzyme. AR-dependent reporter gene assays showed that RL-HSD, RODH 5, and RODH 4 shifted the dose-response curve for 3α-diol a 100-fold, yielding EC50 values of 2.5 × 10−9m, 1.5 × 10−9m, and 1.0 × 10−9m, respectively, when compared with the empty vector (EC50 = 1.9 × 10−7m). Real-time RT-PCR indicated that L-3-hydroxyacyl coenzyme A dehydrogenase and RL-HSD were expressed more than 15-fold higher compared with the other candidate oxidative enzymes in human prostate and that RL-HSD and AR were colocalized in primary prostate stromal cells. The data show that the major oxidative 3α-HSD in normal human prostate is RL-HSD and may be a new therapeutic target for treating prostate diseases.

Sexual differentiation in three unconventional mammals: spotted hyenas, elephants and tammar wallabies

The present review explores sexual differentiation in three non-conventional species: the spotted hyena, the elephant and the tammar wallaby, selected because of the natural challenges they present for contemporary understanding of sexual differentiation. According to the prevailing view of mammalian sexual differentiation, originally proposed by Alfred Jost, secretion of androgen and anti-Mullerian hormone (AMH) by the fetal testes during critical stages of development accounts for the full range of sexually dimorphic urogenital traits observed at birth. Jost's concept was subsequently expanded to encompass sexual differentiation of the brain and behavior. Although the central focus of this review involves urogenital development, we assume that the novel mechanisms described in this article have potentially significant implications for sexual differentiation of brain and behavior, a transposition with precedent in the history of this field. Contrary to the "specific" requirements of Jost's formulation, female spotted hyenas and elephants initially develop male-type external genitalia prior to gonadal differentiation. In addition, the administration of anti-androgens to pregnant female spotted hyenas does not prevent the formation of a scrotum, pseudoscrotum, penis or penile clitoris in the offspring of treated females, although it is not yet clear whether the creation of masculine genitalia involves other steroids or whether there is a genetic mechanism bypassing a hormonal mediator. Wallabies, where sexual differentiation occurs in the pouch after birth, provide the most conclusive evidence for direct genetic control of sexual dimorphism, with the scrotum developing only in males and the pouch and mammary glands only in females, before differentiation of the gonads. The development of the pouch and mammary gland in females and the scrotum in males is controlled by genes on the X chromosome. In keeping with the "expanded" version of Jost's formulation, secretion of androgens by the fetal testes provides the best current account of a broad array of sex differences in reproductive morphology and endocrinology of the spotted hyena, and androgens are essential for development of the prostate and penis of the wallaby. But the essential circulating androgen in the male wallaby is 5alpha androstanediol, locally converted in target tissues to DHT, while in the pregnant female hyena, androstenedione, secreted by the maternal ovary, is converted by the placenta to testosterone (and estradiol) and transferred to the developing fetus. Testicular testosterone certainly seems to be responsible for the behavioral phenomenon of musth in male elephants. Both spotted hyenas and elephants display matrilineal social organization, and, in both species, female genital morphology requires feminine cooperation for successful copulation. We conclude that not all aspects of sexual differentiation have been delegated to testicular hormones in these mammals. In addition, we suggest that research on urogenital development in these non-traditional species directs attention to processes that may well be operating during the sexual differentiation of morphology and behavior in more common laboratory mammals, albeit in less dramatic fashion.

5alpha-Androstane-3alpha,17beta-diol activates pathway that resembles the epidermal growth factor responsive pathways in stimulating human prostate cancer LNCaP cell proliferation

5alpha-Androstane-3alpha,17beta-diol (3alpha-diol) is considered to have no androgenic effects in androgen target organs unless it is oxidized to 5alpha-dihydrotestosterone (5alpha-DHT). We used microarray and bioinformatics to identify and compare 3alpha-diol and 5alpha-DHT responsive gene in human prostate LNCaP cells. Through a procedure called 'hypervariable determination', a similar set of 30 responsive genes involving signal transduction, transcription regulation, and cell proliferation were selected in 5alpha-DHT-, 3alpha-diol-, and epidermal growth factor (EGF)-treated samples. F-means cluster and networking procedures showed that the responsive pattern of these genes was more closely related between 3alpha-diol and EGF than between 5alpha-DHT and 3alpha-diol treatments. We conclude that 3alpha-diol is capable of stimulating prostate cell proliferation by eliciting EGF-like pathway in conjunction with androgen receptor pathway.

Steroid 5alpha-reductase 1 promotes 5alpha-androstane-3alpha,17beta-diol synthesis in immature mouse testes by two pathways

5alpha-Androstane-3alpha,17beta-diol (androstanediol) is the predominant androgen in immature mouse testes, and studies were designed to investigate its pathway of synthesis, the steroid 5alpha-reductase isoenzyme involved in its formation, and whether testicular androstanediol is formed in embryonic mouse testes at the time of male phenotypic development. In 24-26-day-old immature testes, androstanediol is formed by two pathways; the predominant one involves testosterone --> dihydrotestosterone --> androstanediol, and a second utilizes the pathway progesterone --> 5alpha-dihydroprogesterone --> 5alpha-pregnane-3alpha-ol-20-one --> 5alpha-pregnane-3alpha,17alpha-diol-20-one --> androsterone --> androstanediol. Formation of androstanediol was normal in testes from mice deficient in steroid 5alpha-reductase 2 but absent in testes from mice deficient in steroid 5alpha-reductase 1, indicating that isoenzyme 2 is not expressed in day 24-26 testes. The fact that androstenedione and testosterone were the only androgens identified after incubation of day 16 and 17 embryonic testes with [3H]progesterone implies that androstanediol formation in the testis plays no role in male phenotypic differentiation in the mouse.

Partitioning of 5alpha-dihydrotestosterone and 5alpha-androstane-3alpha, 17beta-diol activated pathways for stimulating human prostate cancer LNCaP cell proliferation

The growth and development of the prostate gland are regulated by androgens. Despite our understanding of molecular actions of 5alpha-dihydrotestosterone (5alpha-DHT) in the prostate through the trans-activation of the androgen receptor (AR), comprehensive analysis of androgen responsive genes (ARGs) has just been started. Moreover, expression changes induced by the androgen effects of 5alpha-androstane-3alpha,17beta-diol (3alpha-diol), a metabolite of 5alpha-DHT through the action of 3alpha-hydroxysteroid dehydrogenases (3alpha-HSDs), remain undefined. We demonstrated that both 5alpha-DHT and 3alpha-diol stimulated similar levels of androgen sensitive human prostate cancer LNCaP cell proliferation. However, consistent with the fact that 3alpha-diol has low affinity toward the AR, 3alpha-diol did not elicit the same levels of AR trans-activation activity as that of 5alpha-DHT. Since LNCaP cells respond to androgen stimulation by transcriptionally activating the AR downstream genes, gene expression patterns between 0 and 48 h following 3alpha-diol and 5alpha-DHT stimulation were analyzed using cDNA-based membrane arrays to define the temporal regulation of ARGs. Array analysis identified 217 and 219 androgen-modulated genes in at least one time point following 3alpha-diol and 5alpha-DHTstimulation, respectively, including key regulators of cell proliferation. Only a subset of these genes (143) was regulated by both androgens. These data suggest that 3alpha-diol exerts androgenic effects independent of the action of 5alpha-DHT in steroid target tissues. Accordingly, 3alpha-diol might activate cell proliferation cascades independent of AR pathway in the prostate.

Penile development is initiated in the tammar wallaby pouch young during the period when 5alpha-androstane-3alpha,17beta-diol is secreted by the testes

Virilization of the urogenital tract is under the control of testicular androgens in all mammals. In tammar young, prostate differentiation begins between d 20 and d 40 under the control of the testicular androgen 5alpha-androstane-3alpha,17beta-diol (5alpha-adiol), but uncertainties exist about the control of penile development. We performed longitudinal studies up to d 150 of pouch life to define normal penile development and the effects of androgen administration and castration. In control animals the male phallus was longer than the female phallus by d 48. Closure of the urethra in males begins around d 60 and continues to at least d 150. Administration of supraphysiological doses of testosterone to females caused penile development equivalent to that of the male and also induced partial closure of the urethral groove by d 150. Castration of male pouch young at d 25 prevented penile development, whereas the penis in males castrated at d 40, 80, or 120 had partial closure of the urethral groove. Administration of 5alpha-adiol to females from d 20-40 also caused partial closure of the urethral groove and some growth of the phallus at d 150, whereas 5alpha-adiol treatment from d 40-80 or 80-120 caused some penile growth but had little effect on urethral development. These findings, together with the fact that we found no sex differences in plasma levels of testosterone, dihydrotestosterone, 5alpha-adiol, dehydroepiandrosterone, or androstenedione from d 51-227, clearly indicate that the action of 5alpha-adiol between d 20 and 40 imprints later differentiation of the male penis.

Unsolved problems in male physiology: studies in a marsupial

Testicular androgens induce formation of the male urogenital tract in all mammals. In marsupials male development occurs after birth and over a prolonged period. For example, in the tammar wallaby virilization of the Wolffian ducts begins by day 20, prostate formation begins about day 25, and phallic development starts after day 80 of pouch life. Between days 20 and 40 5alpha-androstane-3alpha,17beta-diol (5alpha-adiol) is formed in tammar testes and secreted into plasma. Administration of 5alpha-adiol to pouch young females induces urogenital sinus virilization by day 40 and formation of a mature male prostate and phallus by day 150. 5alpha-Adiol is synthesized in pouch young testes by two pathways, one involving testosterone and dihydrotestosterone and the other 5alpha-pregnane-3alpha,17alpha-diol-20-one and androsterone as intermediates, both utilizing steroid 5alpha-reductase. In target tissues 5alpha-adiol acts via the androgen receptor after conversion to dihydrotestosterone but may have other actions as well. Whether 5alpha-adiol plays a role in male development in placental mammals is uncertain.

5alpha-androstane-3alpha,17beta-diol is formed in tammar wallaby pouch young testes by a pathway involving 5alpha-pregnane-3alpha,17alpha-diol-20-one as a key intermediate

The synthetic pathway by which 5alpha-androstane-3alpha,17beta-diol (5alpha-adiol) is formed in the testes of tammar wallaby pouch young was investigated by incubating testes from d 20-40 males with various radioactive precursors and analyzing the metabolites by thin-layer chromatography and HPLC. [(3)H]Progesterone was converted to 17-hydroxyprogesterone, which was converted to 5alpha-adiol by two pathways: One involves the formation of testosterone and dihydrotestosterone as intermediates, and the other involves formation of 5alpha-pregnane-3alpha,17alpha-diol-20-one (5alpha-pdiol) and androsterone as intermediates. Formation of 5alpha-adiol from both [(3)H]testosterone and [(3)H]progesterone was blocked by the 5alpha-reductase inhibitor 4MA. The addition of nonradioactive 5alpha-pdiol blocked the conversion of [(3)H]progesterone to 5alpha-adiol, and [(3)H]5alpha-pdiol was efficiently converted to androsterone and 5alpha-adiol. We conclude that expression of steroid 5alpha-reductase in the developing wallaby testes allows formation of 5alpha-reduced androgens by a pathway that does not involve testosterone as an intermediate.

Androgen physiology: unsolved problems at the millennium

Androgen physiology differs from that of other steroid hormones in two major regards. First, testosterone, the predominant circulating testicular androgen, is both an active hormone and a prohormone for the formation of a more active androgen, the 5alpha-reduced steroid dihydrotestosterone. Genetic evidence indicates that testosterone and dihydrotestosterone work via a common intracellular receptor, and studies involving in vitro reporter gene assays and intact mice in which both steroid 5alpha-reductase isoenzymes have been disrupted by homologous recombination indicate that dihydrotestosterone acts during embryonic life to amplify hormonal signals that can be mediated by testosterone at higher concentrations. However, in post-embryonic life dihydrotestosterone plays unique roles that have not been elucidated. Studies of other 5alpha-reduced steroids, including the plant hormone brassinolide, the hog pheromones androstanol and androstenol, and 5alpha-dihydroprogesterone (in horses and elephants) indicate that this reaction serves different functions in different systems. Second, during embryonic life androgen causes the formation of the male urogenital tract and hence is responsible for development of the tissues that serve as the major sites of androgen action in postnatal life. It has been generally assumed that androgens virilize the male fetus by the same mechanisms as in the adult, namely by the conversion of circulating testosterone to dihydrotestosterone in target tissues. However, in marsupial mammals there is no sexual dimorphism in the levels of testosterone or dihydrotestosterone at the time the male phenotype forms, and in the pouch young of one marsupial, the tammar wallaby, the testes secrete another 5alpha-reduced steroid, 5alpha-androstane-3alpha, 17beta-diol (5alpha-adiol), into plasma. The administration of 5alpha-adiol to female pouch young causes profound virilization of the urogenital sinus and external genitalia, but within target tissues 5alpha-adiol appears to work after oxidation to dihydrotestosterone. Thus, two separate mechanisms evolved for the formation of dihydrotestosterone in target tissues. 5alpha-adiol is the predominant androgen in neonatal testes in several placental mammals, but it is unclear whether it plays a similar role in other mammalian species.

Administration of 5alpha-androstane-3alpha,17beta-diol to female tammar wallaby pouch young causes development of a mature prostate and male urethra

Secretion of 5alpha-androstane-3alpha,17beta-diol (5alpha-adiol) by the testes of the tammar wallaby is responsible for initiation of prostatic development after d 20 in male pouch young. To ascertain the role of this hormone in the subsequent growth and differentiation of the prostate and in the development of the male phallus, 5alpha-adiol was administered to tammar female pouch young in two regimens. Administration of the hormone by mouth (8 microg/g body weight.wk) between d 70 and 150 of pouch life caused prostate development equivalent to that in d 150 males and promoted growth and differentiation of the penis, but not masculinization of the urethra. Treatment with a small dose of 5alpha-adiol enanthate (1 microg/g body weight.wk) from d 20-150 produced similar results. However, administration of larger doses of 5alpha-adiol enanthate (10 or 100 microg/g body weight.wk) from d 20-150 caused supraphysiological growth of the prostate, development of a male-type urethra, and penile growth. These results indicate that prostatic development and penile growth can be initiated over a wide time period, but that formation of a male urethra requires androgen action before d 70, when male penile differentiation begins. This further strengthens the hypothesis that 5alpha-adiol is the circulating androgen responsible in this species for virilization during development.

The marsupial model for male phenotypic development

In all mammals, androgen formed in the developing testes is responsible for the aspects of male development in which the Wolffian ducts, urogenital sinus and urogenital tubercle are transformed into the epididymis/vas deferens, prostate and penis. That these events take place after birth in the marsupial makes it possible to examine male phenotypic development during pouch life. In the tammar wallaby, Macropus eugenii, the testicular androgen 5 alpha-androstane-3 alpha,17 beta-diol (5 alpha-adiol) is formed in the developing testis, is secreted into plasma and has the capacity to virilize female young pouch when administered exogenously. 5 alpha-Adiol is formed by immature testes in many species and appears to act in target tissues once it has been converted to dihydrotestosterone.